Mighty Blow
渾身の一撃 [konshin no ichigeki] or 'blow with all one's might' in Japanese.
Record Keeper

Mighty Blow (Soul Break)
Type: Soul Break, Rarity: -
Target: single, Element: -, Gauge cost: 1 bar
Learn: all (equip Black Belt Gi (IV))
Effect: Deals a physical attack
Other: yes, there are two abilities in FFRK called exactly the same, only one of them is a Soul Break and one is a Record Materia

Mighty Blow (Record Materia)
Type: Record Materia, Record Materia Level: 2, Rarity: -
Obtain: drops with a set percentage chance during battle when a Limit Broken Viking is in the party
Effect: Attack becomes Charge
Category: Ability